We demonstrate a lead selenide material sensitization method using O+ beam implantation at 50 keV. A nano-polycrystalline material with similar to 29 nm grain size is synthesized, which is completely different with the currently diffused material in submicron scale. This nano-material exhibits high carrier mobility and optical absorption with an Urbach energy as low as 29.5 meV, indicating a well-ordered microstructure. The responsivity of up to similar to 2 A/W at 4 mu m is achieved for sample with implantation dose of 1 9 10 18 cm(-2). It is revealed that the high responsivity may be attributed to the high optical absorption and carrier mobility.